Great Western Main Line electrification - ongoing discussion

[whole diary]

[TonyK]

300 Amps is not an usual peak starting current for intercity type trains

7.5 MW is a lot to ask of diesel engines, especially when it is needed only for a burst to overcome inertia. There are two ways of looking at the effect of having bi-mode IEPs^▸ (Intercity Express Program / Project.), though. One could say that they are a blessing, because they allow IEPs to penetrate further into the uncharted wilderness that lies outside of the M25. Or one could say that they are an excuse for not finishing the job of electrifying the GWR^▸ (Great Western Railway) completely, and therefore kicking the can down the road yet again. As for blaming Network Rail - I am sure they would have been happy to finish the job, had DafT let them.

[Electric train]

300 Amps is not an usual peak starting current for intercity type trains

7.5 MW is a lot to ask of diesel engines, especially when it is needed only for a burst to overcome inertia. There are two ways of looking at the effect of having bi-mode IEPs^▸ (Intercity Express Program / Project.), though. One could say that they are a blessing, because they allow IEPs to penetrate further into the uncharted wilderness that lies outside of the M25. Or one could say that they are an excuse for not finishing the job of electrifying the GWR^▸ (Great Western Railway) completely, and therefore kicking the can down the road yet again. As for blaming Network Rail - I am sure they would have been happy to finish the job, had DafT let them.

I agree that a rolling stock based diesel will unlikely be viable to produce 7.5MW  This is the advantage of electrification via fixed equipment (OLE^▸ (Overhead Line Equipment, more often "OHLE") / third rail etc)  750V dc is typically limited to 6kA (4.5MW) the dc circuit breakers are typically set to 4 or 6kA a few places they are set to 7kA.  Rolling stock is also programmed to the max for the route even in multiple the overall will not exceed the route max.  The same is done for most ac traction a max current is set for the route, there are some issues with multiple loco's on some freight services where they the FoC has not set the current limit this cause the substation circuit breakers to trip or worse case the wire burns down.

Back to the point, electrification will always provide a quicker acceleration that diesel; the IEP's were originally intended to provide some capability to operate off wired routes, allow for diversions, operate a service when the OLE is not powered and emergency moves; like all things there has been mission creep

[SandTEngineer]

It would appear from info elsewhere that the 25kv was switched on in the Severn Tunnel earlier today.  Under test for a period.

[johnneyw]

It would appear from info elsewhere that the 25kv was switched on in the Severn Tunnel earlier today.  Under test for a period.

So where are things regarding the previous reports of the corrosion of OHLE in the tunnel?

[grahame]

It would appear from info elsewhere that the 25kv was switched on in the Severn Tunnel earlier today.  Under test for a period.

So where are things regarding the previous reports of the corrosion of OHLE in the tunnel?

"Corrosion" may not be accurate.   According to top ponchos at GWR^▸ (Great Western Railway) and Network Rail, the problem was a deposit of unidentified 'summat' on the insulators - with the 'summat' being conductive.  If the research we were told about quickly identified the 'summat' (and, really, how long should it take?) then cleaning it off and taking steps either to clean regularly of stop it coming back is going to be a darned site quicker / easier / cheaper than replacing something that's corroded.

[stuving]

   According to top ponchos at GWR^▸ (Great Western Railway) and Network Rail...

Waterproof ponchos are , of course, essential PPE for any work in the tunnel - and inspecting or cleaning anything overhead calls for a top poncho as well.

[chuffed]

I thought the reference to 'top poncho' was as, in 'covering up'

[Chris125]

So where are things regarding the previous reports of the corrosion of OHLE in the tunnel?

F&F's Noel Dolphin has tweeted the following about the wires being switched-on, and what they did to allow this: https://twitter.com/NoelDolphin


"Severn Tunnel is currently live & electrified at 25kv for the first time. For testing in the run up to full switch on later this year"

"Mainly by removing copper contact wire and using aluminium contact wire. Also fixing some of the leaking drip pans after years of arguing internally in NR^» (Network Rail - home page)."

"Never going to be perfect in those conditions. Will always need more maintenance - as it is almost 100% humidity, permanently in some places. However, most corrosion issues minimised now (would not at this point want to say overcome)"

[SandTEngineer]

Interesting stuff.  Not wishing to digress but this relevant comment elsewhere got to me a bit as I worked in the box there once and remember it going up.......

Also, a moments silence though for whichever genius designed the termination of the electrification wires at St Pancras in the... 80s???

It's more or less forgotten and I can't even find a photo of it.

....and this one from Roger Ford cheered me up afterwards.....

In Scotland they spell Decarbonisation as E-L-E-C-T-R-I-F-Y.  So should we all.

[Adrian]

So where are things regarding the previous reports of the corrosion of OHLE in the tunnel?

F&F's Noel Dolphin has tweeted the following about the wires being switched-on, and what they did to allow this: https://twitter.com/NoelDolphin


"Severn Tunnel is currently live & electrified at 25kv for the first time. For testing in the run up to full switch on later this year"

"Mainly by removing copper contact wire and using aluminium contact wire. Also fixing some of the leaking drip pans after years of arguing internally in NR^» (Network Rail - home page)."

"Never going to be perfect in those conditions. Will always need more maintenance - as it is almost 100% humidity, permanently in some places. However, most corrosion issues minimised now (would not at this point want to say overcome)"

I thought the Severn Tunnel had something more like a rigid metal bar than a normal contact wire?

Is the idea of using aluminium instead of copper that it's a more reactive metal than steel, and therefore it is the aluminium which will preferentially corrode?  Which I suppose is better if the corrosion is not then be concentrated at the point where the OHLE is fixed to the tunnel.

[stuving]

I thought the Severn Tunnel had something more like a rigid metal bar than a normal contact wire?

Is the idea of using aluminium instead of copper that it's a more reactive metal than steel, and therefore it is the aluminium which will preferentially corrode?  Which I suppose is better if the corrosion is not then be concentrated at the point where the OHLE is fixed to the tunnel.

In the F+F ROCS^▸ (Rigid Overhead Conductor System) system (which I presume is what's been used), the actual contact with the pantograph is made by a wire. This is clamped in the base of the rigid "rail" - actually a hollow aluminum section. That can be replaced when it wears, like any other contact wire. It also provides for the transition to the standard suspended OLE^▸ (Overhead Line Equipment, more often "OHLE").

For "damp" sites, they offer plastic covers for the rail and a special grease to waterproof the copper wire/rail contact and prevent corrosion. It seems that the Severn Tunnel is wetter and nastier than that level of "damp". Using aluminum wire will remove the electrochemical corrosion (due to potential differences between dissimilar metals) - how completely will no doubt depend on the alloy used.

[MVR S&T]

Could stainless steel/plastics not be used? I have had lots of problem with Aluminium alloys in damp eletrical boxes.

[ellendune]

Could stainless steel/plastics not be used? I have had lots of problem with Aluminium alloys in damp eletrical boxes.

If I have understood correctly it is the conductor wire that has been changed.  Stainless steel is a poor conductor compared to copper or aluminium so could not be used for the conductor wire. Aluminium is a very good conductor. 

[onthecushions]

Aluminium and its alloys have an unusual behaviour in corrosion.

It has a low hydrogen electrode potential and a heat of combustion about 30% higher than sodium metal (which catches fire in water - pinching the oxygen from the hydrogen!). However it is so reactive that it coats itself immediately with a layer of impervious Aluminuim oxide - called a passive film. Thus Aluminium (Al) panels do not need painting, unless the film is damaged and interrupted such as by scratching or more likely by chemicals such as the chloride ion in saline environments. Thus marine Al rapidly turns to white powder.

We shall see whether the metal survives but tunnels are severe environments for most metals - Merseyrail has had many problems just with steel track, albeit sharply curved. The Seven Tunnel will become a lot cleaner and the heavy gradients better addressed if the OLE^▸ (Overhead Line Equipment, more often "OHLE") works well.

Fingers crossed.

OTC

[CyclingSid]

Aluminium has a higher resistance than copper. Hopefully nothing more than the fact that the electricity meter will turn more for each train.

Worked for a company who made electrical furnances and the like, hundreds of volts and hundreds of amps. Some bright spark (pun intended) in purchasing thought it a good deal to get some cheap cable, which happened to be aluminium. All sorts of problems ensued, especially for the person in purchasing.